1. Field of the Invention
This invention relates to power splitters in general and more particularly to a two way 180 degree power splitter having a small package size.
2. Description of the Prior Art
Power splitters operating at frequencies below 1GHz have been made with ferrite transformers along with appropriate resistors and capacitors arranged around the ferrite transformer. These splitters provide multi-decade bandwidth. The power splitter components are packaged on a printed circuit board. In some applications, printed circuit board space can be extremely limited with additional space just not available. In some applications, it is desirable to build multiple output-port splitters such as 4-way and 8-way by cascading the splitters. Unfortunately, placing resistors and capacitors beside each transformer complicates the assembly program followed by the automated pick and place surface mount assembly equipment. This leads to lower production by the assembly machinery.
FIG. 1 shows a schematic of a prior art 2 way 180 degree power splitter circuit for frequencies of 1-750 MHz. Circuit 20 has transformers T1, T2, T3 and T4. Transformer T1 is connected between ground and an input terminal IN. Transformer T2 has one end connected to winding W1 of transformer T3 and the other end connected to winding W3 of transformer T4. The mid-points of transformers T1 and T2 are connected to ground through a capacitor C1. A resistor R1 is connected across transformer T2. Transformer T3 has a windings W1 and W2. Winding W1 is connected between transformer T2 and output terminal OUT2. Winding W2 has both ends connected to ground. Transformer T4 has windings W3 and W4. Winding W3 is connected between transformer T2 and ground. Winding W4 has one end connected to ground and the other end connected to output terminal OUT1. The circuit of FIG. 1 is a 2 way power splitter that provides an output signal that has 0 degrees of phase shift at terminal OUT2 and 180 degrees of phase shift at terminal OUT1. The circuit of FIG. 1 requires four transformers to perform the power splitting function.
While power splitters have been used, they have suffered from taking up excessive printed circuit board space and in having multiple transformers that add expense and complexity to manufacturing. A current unmet need exists for a power splitter that takes up less printed circuit board space with fewer components that can be easily assembled.
It is a feature of the invention to provide a power splitter having a small package size that has repeatable electrical characteristics.
Another feature of the invention is to provide a power splitter that includes a substrate having several layers. The substrate has a first and a second outer surface. A resistor is formed on the first outer surface. A ground plane is formed on one of the layers. One or more capacitor electrodes are located on one of the layers. The capacitor electrodes form a capacitor. Several terminals are located on the first and second outer surfaces. A transformer is attached to the first outer surface and is electrically connected to the terminals, the resistor, the capacitor and the ground plane. The transformer provides impedance matching and dividing. Several vias extend between the layers to provide an electrical connection between the resistor, the capacitor, the terminals, the ground plane and the transformer.
Another feature of the invention is to provide a power splitter that takes up less printed circuit board space and has improved electrical repeatability.
A further object of the invention is to provide a method of manufacturing a 180 degree power splitter.